The present invention relates to a cannulated drill bit with radially offset cutting edge. In the performance of orthopedic surgery such as, for example, a surgery known as double bundle ACL reconstruction, one procedure required to be performed is that of drilling a graft tunnel hole for the posterior lateral graft bundle in the lateral condyle of the femur. In order to perform this drilling procedure to the greatest advantage, it is best to place the tunnel sufficiently posterior to provide a proper location for the graft.
In so drilling the tunnel, it has been found that it is most advantageous to pass the drill bit as close as possible to the medial femoral condyle so that the hole is drilled in the most proper location.
Currently, drill bits that are employed have an axis of rotation that is the same for both the proximal and distal ends thereof. The proximal end of the drill bit is coupled to a drill that facilitates rotation of the proximal end about its axis of rotation. The distal portion of the drill bit has cutting surfaces that permit creation of the tunnel. The prior art drill bit is cannulated and is guided by a guide wire that may first cut a pilot hole for the graft tunnel hole, then guide the bit in enlarging the pilot hole. With known drill bits, the periphery of the distal portion, which extends about the circumference of the drill bit (FIG. 1), limits the ability to pass the drill bit close enough to the medial femoral condyle to optimize the location where the tunnel hole is created.
In the prior art, the usual technique employed involves passing a guidewire past the medial femoral condyle and into the posterior distal portion of the lateral notch to form the pilot hole. When this technique is employed, it is advantageous to place the guidewire deliberately close to the medial femoral condyle, however, using prior art drill bits, the closest the guidewire may be placed is limited to the drill bit radius plus the appropriate clearance between the periphery of the drill bit and the medial femoral condyle. For example, if a 10 mm drill bit is used (FIG. 1), this clearance is typically 1-2 mm, making the distance of the axis of rotation of the drill from the medial femoral condyle in the range of 5.5 to 6.5 mm. With such a close clearance, it is quite possible, if not probable, that the medial femoral condyle will interfere with proper placement of the periphery of the drill bit. In order to prevent damage to the medial condyle, sometimes, surgeons utilize a thin walled metal or other rigid “protector” used to shield the medial femoral condyle from the periphery of the drill bit. Of course, the shield has a finite thickness that may require increased spacing between the drill bit and the medial femoral condyle. Additionally, use of the “protector” introduces an additional aspect of complication to the procedure, which surgeons prefer to avoid.
As such, it would be advantageous if a system and procedure could be devised that would allow closer spacing between the drill bit and the medial femoral condyle so that the graft tunnel hole for the posterior lateral graft bundle could be placed in closer proximity to the deepest portion of the distal femoral notch.
It is with these thoughts in mind that the present invention was developed.
U.S. Published Patent Application No. US 2004/0220577 A1 to Cragg et al. discloses methods and apparatus for forming shaped axial bores through spinal vertebrae. Cragg et al. teach, in FIGS. 23 and 24 thereof, a drive shaft 236 to which is affixed a spherical drill bit 220 which is slightly offset from the axis of the drive shaft 236. However, as particularly shown in the figures, the ball 220 extends outside the entire periphery of the drive shaft and, as such, could not possibly achieve the goals and advantages of the present invention.